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1 hour ago, Toxn said:

I've run some preliminary numbers on the 'blended' XM-8. At 45 tonnes you get:

  • 145mm aluminium + 500mm NERA @ 45’ (upper hull front): estimated 670mm/970mm LoS KE/chem protection
  • 70mm aluminium @ + 250mm NERA 45’ (lower hull front): estimated 330mm/480mm LoS KE/chem protection
  • 65mm aluminium + 250mm NERA (hull side forward): estimated 160mm/230mm LoS KE/chem protection
  • 25mm aluminium (hull side rear)
  • 25mm aluminium (hull rear)
  • 25mm aluminium (hull roof)
  • 25mm aluminium (hull floor)
  • 175mm aluminium + 500mm NERA @ 30’ (turret front): estimated 560mm/810mm LoS KE/chem protection
  • 65mm aluminium + 250mm NERA (turret side forward): estimated 240mm/350mm LoS KE/chem protection
  • 65mm aluminium + 250mm NERA (turret side rear): estimated 240mm/350mm LoS KE/chem protection
  • 25mm aluminium (turret rear)
  • 200mm aluminium + 500mm NERA (mantlet): estimated 470mm/720mm LoS KE/chem protection
  • 35mm aluminium + 65mm NERA @ 80’ (turret roof forward): estimated 310mm/410mm LoS KE/chem protection
  • 25mm aluminium (turret roof rear)

Result: XM-8E1 is going to have to be a thing.

 

 

LOL, suddenly NERA!

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Just now, Sturgeon said:

 

OK, be honest, did you start adding NERA just out of coincidence or because I put NERA on the Roach submission? XD

I left giant air spaces in my previous hull designs for a reason, son.

 

This isn't going to be for the "present day" version of the design though. Because NERA is unnecessary when your enemies are using AP, APCR and 1st-gen HEAT.

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4 minutes ago, Toxn said:

I left giant air spaces in my previous hull designs for a reason, son.

 

This isn't going to be for the "present day" version of the design though. Because NERA is unnecessary when your enemies are using AP, APCR and 1st-gen HEAT.

 

I just noticed there wasn't any NERA on your M8 submission, is all. Wondered if I caused an "oh shit" moment. I kinda figured everybody would have a bag of tricks they would start throwing out there towards the end of the competition, and NERA is one of the more obvious ones.

Yeah, same for the Roach. "Canonically" it doesn't get NERA until the A5 version, which is from the late 2260s. But it's more for cost and necessity (as in, there is none) reasons than anything else.

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On 9/8/2018 at 12:18 PM, Toxn said:

So here is what we have so far:

o6i2bZR.jpg

The suspension is supposed to get replaced at some point (with external torsion bars), and the rear hull needs reworking.

Plans to make the hull lower, shorter and thinner failed: I ended up using up all the freed space by putting in those crazy modular armour compartments and ended up haing to make the whole thing longer and taller to fit the driver's vision devices in (the poor bastard still has to enter/exit via the turret or the bottom escape hatch) once I'd lengthened the turret. The turret is currently missing the mantlet and coax.

 

The gun is a smooth-bore 120mm/L35 piece which is limited (for now) to firing modified mortar shells at lower velocities (~600 m/s) ala the 8cm PAW 600. The HEAT shell should be able to do ~240mm of penetration even with crappy WW2-era HEAT designs thanks to the lack of spin. The turret actually has 4 crew members crammed into it - one to act as a dedicated rangefinder operator. I have no idea what the elevation/depression on the gun is, but I plan to mess with the turret until it's -10/+30. The gun is massively overbuilt for what it's currently doing, and should be capable of slinging proper HEAT-FS and APFSDS whenever that comes online. The casing for the shell is about 850mm long, so there's lot's of room to play with.

 

The weight without anything in the armour compartments is about 25t, with all the suspension/transmission components rated for 45t. The armour compartments are designed to cover up to the rear of the turret ring in a 45' arc and attacks directly to the side of the crew compartment. The base armour is pretty much nothing (20mm, 500mm air gap and 10mm front plate) but will keep HMGs and early HEAT rockets out. When fully loaded up with modern NERA, however, this thing should be able to keep modern HEAT weapons and previous-gen APFSDS at bay.

@Sturgeon observe.

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7 minutes ago, Sturgeon said:

 

I just noticed there wasn't any NERA on your M8 submission, is all. Wondered if I caused an "oh shit" moment. I kinda figured everybody would have a bag of tricks they would start throwing out there towards the end of the competition, and NERA is one of the more obvious ones.

Yeah, same for the Roach. "Canonically" it doesn't get NERA until the A5 version, which is from the late 2260s. But it's more for cost and necessity (as in, there is none) reasons than anything else.

As I said, NERA and ERA just don't add that much value until second-gen HEAT and APFSDS come along. Until then I think you're still better off with monolithic armour and normal spaced armour for protection.

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2 minutes ago, Toxn said:

No worries.

 

The XM-16 ideas got worked back into the XM-8 before being mostly eliminated in favour of my steel version/aluminium version concept.

 

I actually have no idea how much protection my NERA arrays would offer. They are a little smaller than yours in some areas but backed by more steel.

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7 minutes ago, Sturgeon said:

 

I actually have no idea how much protection my NERA arrays would offer. They are a little smaller than yours in some areas but backed by more steel.

The figures I've been using are a TE of around 0.7 against KE and 1.15 againt HEAT. I have no idea how accurate this is.

 

Edit: that's for chobham-esque NERA, mind. Burlington is more like 0.4/0.9 iirc.

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17 minutes ago, Xoon said:

Out of curiosity, wouldn't the spaced armor on the hull cause APC rounds that do not shatter to have increased penetration? 

I'm not sure how that would work, but my understanding is that spaced armour wouldn't be that effective against solid shot simply because thinner plates of a given hardness/composition etc tend to be less effective than thicker ones where lower-velocity solid projectiles are concerned.

 

So the plates would do some good ITO decapping, setting off fuses and so on. But they'd be less mass efficient against AP then simply increasing the base armour by an equivalent amount.

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14 minutes ago, Toxn said:

APCR, on the other hand...

 

Yep, historical APCR got wrecked by spaced armor.

 

On 9/9/2018 at 4:34 PM, Collimatrix said:

The TL:DR of this 1950s report on spaced armor and other sources I've read is:

 

 

APCR: Totally fucked by even small stand-off plates parallel to the main armor in hasty add-on packages.  Most APCR projectiles had too brittle a core to deal with anything but homogenous armor.

HEAT:  Early HEAT was adversely affected by spaced armor, but by early 1950s level of HEAT projectile optimization it almost ignored it, or even got a slight penetration boost vs spaced armor.  Arrays of many thin plates were modestly more effective vs. HEAT.

APDS:  Adversely affected by spaced armor, but far less than APCR thanks to sheathe designs that protected the core from shattering.

APFSDS:  Early APFSDS was fucked by spaced armor quite badly, but metallurgical improvements meant that later rounds largely ignored it.

APCBC:  Effects heavily dependent on the optimization of the spaced armor array and quality of the rounds.  Well-constructed APCBC is actually more effective against simple spaced armor arrays than against homogeneous plate.  Poorly constructed APCBC suffers against simple stand-off plates almost to the extent that APCR does.  Geometrically well-optimized arrays are moderately more effective on a weight basis against APCBC than homogeneous plate.

 

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2 hours ago, Toxn said:

I'm not sure how that would work, but my understanding is that spaced armour wouldn't be that effective against solid shot simply because thinner plates of a given hardness/composition etc tend to be less effective than thicker ones where lower-velocity solid projectiles are concerned.

 

So the plates would do some good ITO decapping, setting off fuses and so on. But they'd be less mass efficient against AP then simply increasing the base armour by an equivalent amount.

Having the plates parallel to each other causes a slight yawing in the projectile into the plate, effectively reducing the sloping of the main plate.  This is why they found reverse sloped spaced armor to be the most effective, it is however, not very space efficient (see my prototype frontal armor. 

 

A side question to the OP, what type of projectile does the enemies of the Cascadia use? Mainly APCR like Cascaida? 

 

 

Also, aluminum/steel spaced armor:
cWz5Ich.png

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I keep forgetting just how tiny the Cascade Republic is ITO population. For reference; we're talking about a state which, if at its 1940's population level, would be half the size of 1940s Switzerland. If at 1990's levels, then we're looking at a population a quarter of that of 1940s Italy.

 

I think the total tank park is going to be on the order of 100-1000 vehicles.

 

 

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1 hour ago, Toxn said:

I keep forgetting just how tiny the Cascade Republic is ITO population. For reference; we're talking about a state which, if at its 1940's population level, would be half the size of 1940s Switzerland. If at 1990's levels, then we're looking at a population a quarter of that of 1940s Italy.

 

I think the total tank park is going to be on the order of 100-1000 vehicles.

 

 

 

CR has 4.5 mil people, which is a bit bigger than 1940s Switzerland. Yes, I don't expect them to have too many tanks (California will have more) - which is why I think having superior tanks is such a priority.

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9 minutes ago, Sturgeon said:

 

CR has 4.5 mil people, which is a bit bigger than 1940s Switzerland. Yes, I don't expect them to have too many tanks (California will have more) - which is why I think having superior tanks is such a priority.

I agree - my estimates put the Californians at something like 7-8 million strong, so you're pretty much stuck with a defensive war there and hoping to inflict disproportionate casualties.

 

The largest tank battles are going to look those in Indo-Pakistan '65: maybe 300 vehicles all told. Most battles will be much smaller, perhaps a few dozen vehicles.

 

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11 minutes ago, Toxn said:

I agree - my estimates put the Californians at something like 7-8 million strong, so you're pretty much stuck with a defensive war there and hoping to inflict disproportionate casualties.

 

The largest tank battles are going to look those in Indo-Pakistan '65: maybe 300 vehicles all told. Most battles will be much smaller, perhaps a few dozen vehicles.

 

 

Sounds about right.

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On 8/27/2018 at 7:53 PM, Lord_James said:

I upgraded my Shot mk-1 to Shot mk-2... I now need to make a new gun, but still: 

 

  Reveal hidden contents

KHSIVIM.png

SgBqgOS.png

GJwk1eR.png

 

18.11kg complete shell, 800mm total length, and now has a 130mm bottle shape. 

New propellant mass: 5.25kg 

New velocity: 1207 m/s out the barrel (with 50 caliber barrel). 

projectile is the same as before (5.84kg complete, 275mm length, 50x200mm tungsten carbide slug) 

 

I'm getting penetration values that I believe are a little high (173mm @ 2000m @ 0o), but then again my shell is going hella fast, so IDK. 

 

After doing some research, and some better math, I found different numbers for my shell’s penetration. Using this formula: 

 

image.png.6d7d07faea68bbd268fb63585ffb6a

 

E= energy of projectile 

 

A= armor resistance factor (1960 for tungsten carbide against 240bhn armor steel) 

 

D= Diameter of penetrator (in decimeters) 

 

S= armor thickness 

 

 

And solved for S, you get an equation that will give you a penetration figure for your shell that’s close to RL (I tested 90mm M304 and 76mm M93 and came out to 322mm (12.68 inches) and 235mm (9.25 inches) at PB, respectively). Using this and the data I got from JBM and the load calculator for my projectile, I am now getting numbers that look like: 

 

point blank: 

447mm @ 0* 

335mm @ 30* 

 

2000m: 

232mm @ 0* 

174mm @ 30* 

 

 

I am now pondering how I made a weapon so poweful by mistake, but then again my shell is over 1kg heavier, and moving about 200m/s faster, that M304, so I guess it makes sense that my shell would penetrate more armor. 

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